The demonstration set yields a fair estimate of air permeability µair from coil data¶

Claim · All claims
Evidence · 1 study (2 entries) · design r2 · q2 · i1 small
Currency · newest study 2014 · not yet checked against its sources · not reviewed by a person · overdue for a recheck since 2017: tool and model accuracy changes quickly

Subclaims¶

q2 i? A fit with b fixed at −3 returns a′ = 4240± 25.81, leading to µair∼= 1.298× 10−6Hm−1, in good agreement with the expected µ0. → V.O.M. Lara 2014 q2 i? A point-by-point error analysis using the variance propagation formula gives σµair = 0.1× 10−6Hm−1, enabling evaluation of µair with 2 significant figures. → V.O.M. Lara 2014 (2)

Evidence¶

V.O.M. Lara 2014¶

V.O.M. Lara, D. F. Amaral, D. Faria, and L. P. Vieira. (2014). Demonstrations of magnetic phenomena: Measuring the air permeablity using tablets. https://arxiv.org/abs/1405.6581 doi:10.48550/arxiv.1405.6581

q2 · i1 · design · r2

Data fit under the magnetic-dipole model with b imposed at −3, using the coil's mean radius, turns and current; the fit returned a′ = 4240± 25.81 with standard deviation less than 1%, and unit conversion gave "µair∼= 1.298× 10−6Hm−1".

"Converting all the units to their SI values, the result leads to µair∼= 1.298× 10−6Hm−1, in good agreement with the expected value of µ0 ≡ 4π× 10−6 ≈ 1.2566370614× 10−6Hm−1."

V.O.M. Lara 2014 (2)¶

V.O.M. Lara, D. F. Amaral, D. Faria, and L. P. Vieira. (2014). Demonstrations of magnetic phenomena: Measuring the air permeablity using tablets. https://arxiv.org/abs/1405.6581

q2 · i? · the article prints no effect size for this finding · design · r2

A more sophisticated error analysis replacing each Table II coil data point in equation 2, with stated measurement uncertainties and the variance formula; Fig. 6 shows the per-distance µair values deviating relatively little from the expected value.

"The uncertainty σµair = 0.1× 10−6Hm−1 tell us that the experiment enables the evaluation of µair with 2 significant figures."

Discussion¶

Related Claims¶

• The magnet data cannot determine air permeability; only the magnet's dipole moment can be estimated — reports the opposite
• Magnetic field falls off as the inverse cube of axial distance for both a coil and a magnet — a broader claim this one bears on
• Magnetic field measured by a tablet magnetometer depends linearly on the coil current — related